This invention relates to a flux which is employed when parts made of an aluminum alloy are brazed into an article by means of a metallic solder, and especially such a flux which is made of fluorides only and is noncorrosive as it does not contain any chloride.
It has been known that it is advantageous to employ, in brazing aluminum parts, a flux which is composed of fluorides but does not contain any chloride, because its residues are insoluble in water and therefore the aluminum parts so brazed will scarcely be corroded even when they are not washed in water. Hence, in comparison with a traditional brazing method which employs a chloride flux and accordingly absolutely needs washing of aluminum parts in water after they have been brazed and also needs the treatment of waste water, a brazing method with a fluoride flux is become more popular, since this method can save the expense for removing water pollutants.
However, said latter method is accompanied with drawbacks that when aluminum parts contain Mg of more than 0.5%, conventional fluoride fluxes produce a magnesium fluoride having a high melting point, whereby it becomes impossible to braze them with aluminum solders, because they have a melting point lower than that of magnesium fluorides. Although it has been reported that aluminum alloy parts containing Mg can be brazed with the employment of cesium fluorides as a flux, such brazing does not seem practical, because cesium fluorides are extremely expensive.
In view of the above background, it is an object of this invention to provide a noncorrosive flux which is economically employable for brazing aluminum alloy parts contained with Mg.